Boost converter deadtime compensation

ABSTRACT

A hybrid powertrain system may include an electric machine, a battery back, a boost converter and at least one controller. The boost converter may include an inductor and be configured to receive input voltage from the battery back and provide an output voltage to the electric machine. The at least one controller may generate a duty cycle command for the boost converter based on a magnitude of input current to the boost converter and a magnitude of ripple associated with a current through the inductor such that for a given commanded voltage, an actual duty cycle for the boost converter changes depending on a direction of the current through the inductor to drive the output voltage to the given commanded voltage.

TECHNICAL FIELD

This disclosure relates to systems and methods for improving boostconverter output in a hybrid powertrain.

BACKGROUND

Hybrid Electric Vehicles (HEVs) include one or more electric machinesdriven by inverter systems and may include an internal combustionengine. A high voltage battery is used in the electrified powertrain tosupply power to the electric machines and to store energy recuperatedduring vehicle braking. The electric motor/generator(s) within a hybridelectric vehicle provides additional degrees of freedom in deliveringthe driver-demanded torque and may also be used to control the outputspeed of the engine.

It is known that a boost converter may be used in hybrid powertrainsystems for increasing voltage to control the one or more electricmachines while allowing for a reduction in the number of cells needed inthe vehicle battery back. The basic principle of a boost converterconsists of an input side, an output side, switches and three distinctoperating states including a bottom-switch-on-state, atop-switch-on-state, and both-switches-off-state. During thebottom-switch-on-state, the bottom switch is closed resulting in achange in positive direction in the inductor current. During thetop-switch-on-state, the top switch is closed and the bottom switch isopened allowing the inductor current to change direction and travelthrough the top switch to the output side. The switching between thesetwo states results in higher voltage on the output side than input side.To avoid both switches turning on at the same time, aboth-switches-off-state is implemented to insert a delay in time betweenone switch closing and the other switch opening. This delay between theswitch states is called deadtime.

SUMMARY

In a first illustrative embodiment, a hybrid powertrain system mayinclude, but is not limited to, an electric machine, a battery back, aboost converter and at least one controller. The hybrid powertrainsystem boost converter circuit may include an inductor allowing thecircuit configuration to receive input voltage from the battery pack andprovide an output voltage to the electric machine. The hybrid powertrainsystem may program the at least one controller to generate a duty cyclecommand for the boost converter based on a magnitude of input current tothe boost converter and a magnitude of ripple associated with a currentthrough the inductor such that for a given commanded voltage, an actualduty cycle for the boost converter changes depending on a direction ofthe current through the inductor to drive the output voltage to thegiven commanded voltage.

In a second illustrative embodiment, a method for dead-time compensatinga duty cycle command for a boost converter. The method may includeoperating a response to a magnitude of input current for the boostconverter being greater than a sum of a ripple current magnitude throughan inductor of the boost converter and/or a predefined value correlatedwith the boost converter. The method may correct the duty cycle commandbased on a dead-time associated with the boost converter and a directionof an input current to drive an output voltage of the boost converter toa commanded value.

In a third illustrative embodiment, a vehicle may include a boostconverter having an inductor, one or more transistors, diodes and acapacitor. The boost converter may be configured to receive an inputvoltage and provide an output voltage that is greater than the input.The vehicle may have at least one controller programmed to generate aduty cycle command for the boost converter based on a magnitude ofripple associated with a current through the inductor and a magnitude ofcurrent sufficient to reveal a polarity of the current such that for agiven commanded voltage, an actual duty cycle for the boost converterincreases as the current becomes positive and decreases as the currentbecomes negative. The controller is programmed to generate the boostconverter duty cycle command to drive the output voltage to the givencommanded voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a hybrid electric vehicle (HEV);

FIG. 2 is a schematic diagram of electric machines and associated powerelectronics and control electronics;

FIG. 3 is a schematic diagram of a boost converter circuit;

FIG. 4 is a graph of a duty cycle for a boost converter according;

FIG. 5 is a flowchart of an algorithm for determining a corrective dutycycle for a boost converter circuit; and

FIG. 6 is a graph of a corrective duty cycle for a boost converter.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

The embodiments of the present disclosure generally provide for aplurality of circuits or other electrical devices. All references to thecircuits and other electrical devices and the functionality provided byeach are not intended to be limited to encompassing only what isillustrated and described herein. While particular labels may beassigned to the various circuits or other electrical devices disclosed,such labels are not intended to limit the scope of operation for thecircuits and the other electrical devices. Such circuits and otherelectrical devices may be combined with each other and/or separated inany manner based on the particular type of electrical implementationthat is desired. It is recognized that any circuit or other electricaldevice disclosed herein may include any number of microprocessors,integrated circuits, memory devices (e.g., FLASH, RAM, ROM, EPROM,EEPROM, or other suitable variants thereof) and software which co-actwith one another to perform any number of the operation(s) as disclosedherein.

Referring now to the drawings, FIG. 1 is a schematic representation of avehicle 10, which may include an engine 12 and an electric machine, orgenerator 14. The engine 12 and the generator 14 may be connectedthrough a power transfer arrangement, which in this embodiment, is aplanetary gear arrangement 16. Of course, other types of power transferarrangements, including other gear sets and transmissions, may be usedto connect the engine 12 to the generator 14. The planetary geararrangement 16 includes a ring gear 18, a carrier 20, planet gears 22,and a sun gear 24.

The generator 14 can also output torque to a shaft 26 connected to thesun gear 24. Similarly, the engine 12 can output torque to a crankshaft28, which may be connected to a shaft 30 through a passive clutch 32.The clutch 32 may provide protection against over-torque conditions. Theshaft 30 may be connected to the carrier 20 of the planetary geararrangement 16, and the ring gear 18 may be connected to a shaft 34,which may be connected to a first set of vehicle drive wheels, orprimary drive wheels 36 through a gear set 38.

The vehicle 10 may include a second electric machine, or motor 40, whichcan be used to output torque to a shaft 42 connected to the gear set 38.Other vehicles within the scope of the present application may havedifferent electric machine arrangements, such as more or fewer than twoelectric machines. In the embodiment shown in FIG. 1, the electricmachine arrangement (i.e., the motor 40 and the generator 14) can bothbe used as motors to output torque. Alternatively, each can also be usedas a generator, outputting electrical power to a high voltage bus 44 andto an energy storage system 46, which may include a battery pack 48 anda battery control module (BCM) 50.

The battery 48 may be a high voltage battery that is capable ofoutputting electrical power to operate the motor 40 and the generator14. The BCM 50 may act as a controller for the battery 48. Other typesof energy storage systems can be used with a vehicle, such as thevehicle 10. For example, a device such as a capacitor can be used, whichlike a high voltage battery is capable of both storing and outputtingelectrical energy. Alternatively, a device such as a fuel cell may beused in conjunction with a battery and/or capacitor to provideelectrical power for the vehicle 10.

As shown in FIG. 1, the motor 40, the generator 14, the planetary geararrangement 16, and a portion of the second gear set 38 may generally bereferred to as a transmission 52. Although depicted as a powersplitdevice in FIG. 1, other HEV powertrain configurations may be employed,such as parallel or series HEVs. To control the engine 12 and componentsof the transmission 52 (e.g., the generator 14 and motor 40), a vehiclecontrol module 54, such as a powertrain control module (PCM), may beprovided. The control module 54 may include a vehicle system controller(VSC), shown generally as controller 56. Although it is shown as asingle controller, the controller 56 may include controllers that may beused to control multiple vehicle systems. The control module 54 mayinclude both software embedded within the controller 56 and/or separatehardware to control various vehicle systems.

A controller area network (CAN) 58 may allow the controller 56 tocommunicate with the transmission 52 and the BCM 50. Just as the battery48 includes a BCM 50, other devices controlled by the controller 56 mayhave their own controllers. For example, an engine control unit (ECU) 60may communicate with the controller 56 and may perform control functionson the engine 12. In addition, the transmission 52 may include atransmission control module (TCM) 62, configured to coordinate controlof specific components within the transmission 52, such as the generator14 and/or the motor 40. Some or all of these various controllers canmake up a control system in accordance with the present application.Although illustrated and described in the context of the vehicle 10,which is a HEV, it is understood that embodiments of the presentapplication may be implemented on other types of vehicles, such as aplug-in hybrid electric vehicles (PHEV) or those powered by an electricmotor alone.

Also shown in FIG. 1 are simplified schematic representations of abraking system 64, an accelerator pedal 66, and a gear shifter 68. Thebraking system 64 may include such things as a brake pedal, positionsensors, pressure sensors, or some combination thereof (not shown) aswell as a mechanical connection to the vehicle wheels, such as thewheels 36, to effect friction braking. The braking system 64 may alsoinclude a regenerative braking system, wherein braking energy iscaptured and stored as electrical energy in the battery 48. Similarly,the accelerator pedal 66 may include one or more sensors, which like thesensors in the braking system 64, may communicate information to thecontroller 56, such as accelerator pedal position. The gear shifter 68may also communicate with the controller 56. For instance, the gearshifter may include one or more sensors for communicating the gearshifter position to the controller 56. The vehicle 10 may also include aspeed sensor 70 for communicating vehicle speed to the controller 56.

The engine 12 may be the sole power source in an HEV, such as vehicle10. The battery 48 can, however, operate as an energy storage device.For instance, the battery 48 may store power from the engine 12 that hasbeen converted into electricity by the generator 14. Further, thevehicle's kinetic energy may be transformed into electrical energy bythe motor 40 during braking and stored in the battery 48. The vehicle 10may have two sources of motive force or power: the engine 12 and thebattery 48. The engine 12 may provide mechanical energy to a drivelinevia reaction torque provided by the generator 14. The battery 48 mayprovide electrical energy to the driveline through the motor 40.

The combination of energy provided to the driveline from both the engine12 and the motor 40 may determine the amount of wheel torque (T_(w))applied to the drive wheels 36. For instance, the amount of wheel torque(T_(w)) may be determined based on the sum of engine torque (T_(e)) andmotor torque (T_(m)). While energy produced by the engine 12 and motor40 may be described in terms of power, one of ordinary skill in the artunderstands that power is a function of torque and rotational speedabout an axis, such as engine speed or motor speed.

The controller 56 may receive one or more inputs from a driver, such asaccelerator pedal position, brake pedal position, gear shifter positionand speed control inputs, or the like. Further, the controller 56 mayalso receive feedback signals from one or more subsystem controllers,such as the BCM 50, ECU 60, TCM 62, or the like. The driver inputs andfeedback signals may be used by the controller 56 to determine thecombination of engine power and motor power that may deliver improvedfuel economy, emissions, performance and drivability of the vehicle 10while maintaining state of charge (SOC) of battery 48 and hardwareintegrity. In doing so, the controller 56 may output control signalscorresponding to engine torque, engine speed, wheel torque, or the like.These control signals output from the controller 56 may controlfunctions and/or operating modes of the vehicle 10, such aselectric-only vehicle (EV) mode, hybrid mode, engine start and stop,regenerative braking, engine speed-load operating efficiency, batteryprotection, or the like. As an example, an engine torque command may besent from the controller 56 to the ECU 60 to effectuate operation of theengine 12. As another example, an engine speed command and a wheeltorque command may be sent from the controller 56 to the TCM 62 toeffectuate operation of the generator 14 and motor 40.

As previously described, wheel torque (T_(w)) may correspond to theamount of torque supplied to the drive wheels 36 as requested by adriver via the accelerator pedal, brake pedal and/or gear shifter. Aspreviously mentioned, wheel torque provided to the drive wheels 36 maybe produced by either the engine 12 or the motor 40 powered by thebattery 48, or a combination thereof. However, fuel economy may beimproved by limiting the operation of the engine 12 and, thus, theconsumption of fuel. To this end, the controller 56 may attempt tomaximize EV mode operation, while maintaining battery SOC, and stillprovide sufficient vehicle performance to meet the power demands of thedriver. Accordingly, improved energy efficiency and/or fuel economy maybe realized by maximizing the amount of motor torque (T_(m)) transferredfrom motor 40 to the drive wheels 36 to meet the driver demanded wheeltorque (T_(w)).

Moreover, torque from the motor 40 to the wheels 36 may be obtainedfaster than torque from the engine 12. Stated differently, motor torque(T_(m)) can be generated and transferred to the drive wheels 36 morequickly than engine torque (T_(e)) can be generated and transferred tothe drive wheels 36. Therefore in addition to better fuel economy,improved drivability or vehicle responsiveness to changes in wheeltorque demands may be achieved by using the motor 40 to produce therequested wheel torque. At times, however, the energy available from thebattery 48 to power the motor 40 may not be adequate for the motor 40 togenerate sufficient motor torque to meet potential wheel torque demandsrequested by a driver. When this occurs, the engine 12 may be started tosupplement the maximum available motor torque with engine torque to meetthe driver demanded wheel torque. This may result in decreased vehicledrivability, for instance during acceleration, as the transfer of torquefrom the engine 12 to the drive wheels 36 in response to a driver'srequest may be relatively slow.

In such power limited operating conditions, conventional vehicles canraise engine speed and torque allowing a torque converter to absorb theadditional energy until it is needed. An HEV, such as vehicle 10, maynot include a torque converter. Accordingly, the engine power typicallycannot exceed the power going to the drive wheels 36 minus the maximumallowable battery power that may be used to drive the motor 40 when themotor 40 is being operated at maximum efficiency. In particular, enginepower may not be increased such that the sum of the engine power and theavailable battery power exceeds the requested wheel power. Limits may beplaced on the battery 48, for instance, in order to maintain the batterySOC within a pre-determined range to protect the battery from under andover voltage conditions or to prevent over current conditions. As aresult, the battery power available to drive the motor 40 in order toproduce torque for the drive wheels 36 may be limited.

In order to improve drivability when battery limits are reached, powerfrom the engine 12 may be reduced allowing the electric machines toprovide the power being requested by a driver. In the exemplaryembodiment depicted in FIG. 1, the generator 14 and the motor 40 may betwo synchronous alternating current (AC) electric machines. Accordingly,each electric machine may operate at different efficiencies depending onhow they are driven. Electric machine efficiency may span the range fromfully efficient to fully inefficient. In a fully efficient electricmachine, the maximum possible torque may be produced for a given amountof energy supplied to the machine. In contrast, all of the energysupplied to a fully inefficient electric machine may be dissipated asheat.

The power from the engine 12 may be absorbed in the generator 14 and/ormotor 40 in order to improve drivability when the battery limits arereached. To this end, the motor 40 may be operated inefficiently so thatengine power can be increased to exceed the wheel power minus theavailable battery power required to drive the motor 40 at the requestedtorque. Therefore, by operating the motor 40 inefficiently, engine powermay be increased such that the sum of the engine power and the batterypower available to drive the motor 40 exceeds the requested wheel power.

The additional engine power may be used to offset losses in the motor 40as a result of operating inefficiently. For instance, the additionalengine power may be mechanically applied to the drive wheels 36 tooffset a reduction in output torque of the motor 40. The reduction inoutput torque of the motor 40 may be the result of decreasing motorefficiency without increasing the energy supplied to the motor 40 fromthe battery 48 due to battery limits having been met. Additionally oralternatively, the additional engine power may be converted intoelectrical energy by the generator 14 and output to the high voltage bus44. As a result, the energy input to the motor 40 may be increasedwithout drawing additional energy from the battery 48. Due to theinefficient operation of the motor 40, the additional energy supplied tothe motor 40 from the engine 12 as result of increasing engine power maybe dissipated as heat in the motor 40. Thus, the wheel torque may remainrelatively constant in a limited battery condition despite the reductionin motor efficiency. For the sake of simplicity, efficient operation ofthe motor 40 may be referred to as “normal mode,” whereas inefficientoperation of the motor 40 may be referred to as “lossy mode” even thoughthe degree of inefficiency may vary when the motor 40 is in the lossymode.

The additional losses that can be obtained by operating the motor 40 ina lossy mode may allow for the engine 12 to operate at power levelshigher than without the lossy mode. Consequently, the battery SOC mayremain within set limits while wheel power demands are met. With theengine 12 contributing more system power than requested by a driver andthe excessive power in the system being dissipated as heat in the motor40, the vehicle 10 can quickly react to a driver's acceleration requestby changing the efficiency of the motor 40 from inefficient toefficient, i.e., lossy mode to normal mode. The increase in motorefficiency may result in an immediate increase in output torque of themotor 40, which may be transferred relatively quickly to the drivewheels 36. Accordingly, increased acceleration may be promptly realizedunder both full and reduced battery limits without waiting on the engine12.

The example embodiment in FIG. 2 includes both a motor 40 and agenerator 14. In one embodiment, motor 40 is an electric machine towhich electrical energy is supplied to drive the motor to provide torqueat the motor's output shaft and generator 14 is an electric machine inwhich electric energy is generated due to torque that is applied to ashaft of the generator. In other embodiments, motor 40 and/or generator14 are adapted to operate as both motors and generators. Motor 40 andgenerator 14 are AC electric machines that are coupled to a motorAC-to-DC inverter 114 and a generator AC-to-DC inverter, respectively.In embodiments, in which motor 40 and generator 14 are DC electricmachines, no such inverter is provided. Inverters 114, 116 are coupledto DC-to-DC boost inverter 118, which is in turn coupled to anelectrical storage device, a battery 48. An electric control unit (ECU)24 is provided to manage inverters 114, 116. The ECU may be a separatecontrol module in communication with a vehicle control module and/or maybe embedded with the vehicle control module including, but not limitedto, a powertrain control module, hybrid control module, or atransmission control module. ECU 24 provides control outputs based onsignals indicating an indication of torque demand, i.e., torque command126, from an operator input, possibly from a human operator or anothercontroller. Furthermore, ECU 24 receives inputs from motor 40 andgenerator 14 from which one or more of: speed, torque, current, voltage,etc. can be determined.

FIG. 3 is an illustrative embodiment of a boost converter circuit thatmay be implemented in a hybrid powertrain system. In a hybrid vehicle,the powertrain system may include a boost converter that may be used toprovide a higher voltage for one or more electric machines. The boostconverter circuit may have the following architecture, including, butnot limited to, an input 202, a switch 204, an inductor 206, transistors208 and 210, diodes 212 and 214, a capacitor 216, and an output 218.

When the switch 204 is closed, the boost converter is enabled andengaged by allowing the input 202 to flow through the circuit. The inputvoltage and capacitor 216 may provide the necessary current to theinductor 206. The current may flow through the upper transistor 208, orlower transistor 210 based on the switching cycle between the twotransistors.

The transistors 208 and 210 may include, but are not limited to,insulated-gate bipolar transistors. The transistor(s) configuration inthe boost converter circuit architecture may also be embedded with adiode 212 and 214, or have the diode 212 and 214 independently attached.

Based on the switching cycle of the transistors 212 and 214, the currentalternates flow through the upper transistor 212 and lower transistor214 to provide the higher (boosted) voltage to the output voltage 218.

For example, a boost converter circuit operating state may have aswitching cycle of opening and closing the transistors to allow currentflowing through the inductor to change direction, therefore changingpolarity of current through the inductor. The change in current flowthrough the inductor causes the polarity to be reversed, and as a resultthe input and inductance become in series causing the input voltage andinductance voltage to be combined. The two sources in series cause ahigher voltage to charge the capacitor; therefore the output may alwayshave a voltage greater than that of the input alone.

The operating state may include control of one or more switches to allowalternate direction of current flow to an inductor, therefore causingthe inductor to continuously change polarity. An example of an operatingstate for the boost converter circuit shown in FIG. 3 may consist of abottom-switch-on-state, a top-switch-on-state, andboth-switches-off-state. During the bottom-switch-on-state, the bottomswitch is closed resulting in a change in positive direction in theinductor current. During this state, the capacitor may be able toprovide the voltage and energy to the load while the diodes block anydischarging through the circuit. During the top-switch-on-state, the topswitch is closed and the bottom switch is opened allowing the inductorcurrent to change direction and travel through the top switch to theoutput side. The switching between these two states results in highervoltage on the output side than input side. To avoid both switchesturning on at the same time, a both-switches-off-state is implemented toinsert a delay in time between one switch closing and the other switchopening. The switching cycle is fast enough so that the inductor may notdischarge fully in between switching states.

FIG. 4 depicts an exemplary graph of a duty cycle for a boost converteraccording to one or more embodiments of the present application. Thepulse width modulation (PWM) carrier waveform 306 may be generated by acontrol module commanding a duty cycle for the switching of one or moretransistors in a boost converter circuit. An upper switch duty cyclecommand 302 may be a result of the PWM carrier waveform 306. The upperswitch duty cycle command may be within a switching period 304 as shownin FIG. 4. The switching period 304 is a predefined amount of time thatallows one or more transistors to complete a transition of turning onand off their switches by operating the boost converter based on theduty cycle command.

The upper switch duty cycle command 302 may be delayed based on thedeadtime 318 between the switching states of the upper and lowertransistors. The actual upper switch duty cycle 308 is less than theupper switch duty cycle command 302.

The actual lower switch state 310 may be delayed based on the deadtime318 between the switching states of the upper and lower transistors. Theactual lower switch state 310 is less than the lower duty cycle command,which is not shown. It, however, is the complement of the upper switchduty cycle command 302.

The boost converter circuit is designed so that only one transistor ison at a time during the transition cycle of turning on one transistorwhile turning the other off. The operation of the boost converter maycause inductor current to increase or decrease. The inductor current mayincrease or decrease in the boost converter depending on a duty cyclecommand and/or the current polarity of the inductor. The polarity of thecurrent through the inductor may be in response to the direction of thecurrent though the inductor during a transition between the one or moretransistors in the boost converter circuit.

For example, the inductor current may cross zero 314, therefore thedeadtime 318 in the transition region between the switching states maynot affect boost gain. When the upper transistor switch is turned offbased on the actual upper switch duty cycle 308, the inductor current isnegative so diode 214 is forced to turn on causing current to increase.When the lower switch is turned off, current is positive, forcing diode212 to turn on, causing current to decrease. In this described example,the inductor current crossing zero 314 may represent that deadtime doesnot have an impact to duty cycle.

In another example, when the inductor current is completely positivecurrent 312 the effective duty cycle of the upper transistor switch 308may be shortened by deadtime. The duty cycle for the upper switch may bereduced by the percentage of deadtime of the entire switching cycle. Theinductor current continues to discharge through diode 212 until theactual lower switch duty cycle 310 turns on the lower transistor. Thecharging of the inductor is shortened by the narrow pulse due to thedeadtime 318.

In another example, when the inductor current is completely negativecurrent 316 the deadtime allows for extended charging of the inductor.In this described example, the inductor current completely negative 316may represent that deadtime in the boost converter circuit does not havean impact to duty cycle.

FIG. 5 is an exemplary flowchart depicting a method according to one ormore embodiments of the present disclosure. The method is implementedusing software code contained within the vehicle control module,according to one or more embodiments. In other embodiments, the method400 is implemented in other vehicle controllers, or distributed amongstmultiple vehicle controllers.

Referring again to FIG. 5, the vehicle and its components illustrated inFIGS. 1-3 are referenced throughout the discussion of the method tofacilitate understanding of various aspects of the present invention.The method of controlling the boost converter in the vehicle may beimplemented through a computer algorithm, machine executable code, orsoftware instructions programmed into a suitable programmable logicdevice(s) of the vehicle, such as the vehicle control module, the hybridcontrol module, other controller in communication with vehicle computingsystem, or a combination thereof. Although the various steps shown inthe flowchart diagram 400 appear to occur in a chronological sequence,at least some of the steps may occur in a different order, and somesteps may be performed concurrently or not at all.

At step 402, the vehicle computing system may receive a measurement ofthe direct current (DC) from the boost converter circuit. The value ofthe DC current may be provided by, but not limited to, one or morecurrent sensors located on the input of the boost converter. The valueof the DC current may provide an estimation of power needed at theoutput of the boost converter. Once the value of the DC current has beenreceived and the magnitude of current input to the boost converter iscomprehended by the controller, the system may determine if the currentvalue is more or less than a certain calibratable value or in betweencertain calibratable values.

In one illustrative embodiment, the system may obtain DC current byprojecting current based on the demanded output power using thefollowing equation:ΣT*w/V_(inputbattery)  (0)wherein T is torque command, w is speed of an electric machine, andV_(inputbattery) is input battery voltage.

The system may check the amount of direct current (DC) value todetermine if it is more or less than predefined certain value(s) or inbetween predefined value(s). The predefined value may be based on amagnitude of direct current sufficient to reveal a polarity of currentthrough the inductor. The predefined certain values may include theamount of direct current needed to determine if inductor current is highenough to be considered positive. The system may determine if the DCcurrent at the inductor is a positive value or a negative value based onthe one or more sensor measurements made at the boost converter and/orseveral equation calculations done by a processor. At step 404, thesystem may determine if the duty cycle current value is greater than thesum of current ripple and a predefined calibratable value by thefollowing equation which may include, but is not limited to:

$\begin{matrix}{{I_{DC}} > {I_{ripple} + I_{\frac{delta}{2}}}} & (1)\end{matrix}$wherein |I_(DC)| is the absolute value of the DC current. The I_(ripple)is an equation that includes:

$\begin{matrix}{I_{ripple} = {{DC}_{desired} \times T_{switchingperiod} \times {\frac{V_{output} - V_{inputbattery}}{L_{inductor}}/2}}} & (2)\end{matrix}$wherein DC_(desired) is the desired duty cycle coming from amicrocontroller. The T_(switchingperiod) is the total amount of time itmay take for an on and off cycle for one or more transistors in theboost converter circuit. The V_(output) is the output voltage of theboost converter, and V_(inputbattery) is the input battery voltagereceived by the boost converter circuit. The L_(inductor) is theinductance of the boost converter inductor. The magnitude of current anda magnitude of ripple current associated with the inductor may allow thesystem to determine the direction of the current through the inductorwhile providing the system with a more accurate command ofvoltage/current to the boost converter circuit.

The I_(delta) in equation (1) is a constant selected and/or calibratedbased on the boost converter circuit design to avoid possibleoscillation caused by sudden changes of the boost converter current anddifference between I_(ripple) and real current ripple magnitude. TheI_(delta) may be the predefined amount of DC current needed to determineif inductor current is high enough to be a positive or negative value.The I_(delta) may be a predetermined calibrated or hard coded value insoftware based on the boost converter circuit and/or hybrid powertrainsystem design.

If the DC current is greater, the system may determine corrective dutycycle at step 406. Taking into account the greater current duty cycle,the system may determine a corrective duty cycle based on the followingcalculated equation:Corrective_(dutycycle) =DC _(deadtime) sgn((I _(DC))  (3)wherein DC_(deadtime) is the duty cycle deadtime which is a constant anddetermined by the boost converter circuit design, and sgn(I_(DC)) is thesignum function of the measured duty cycle current. TheCorrective_(dutycyle) may be added to desired duty cycle DC_(desired)allowing the boost converter to reduce and/or remove voltage spikes atthe boost converter output.

At step 408, if the DC current is less than

${I_{ripple} + I_{\frac{delta}{2}}},$then the system may determine if the value is negative or crossing zerousing the following equation:

$\begin{matrix}{{I_{DC}} < {I_{ripple} - I_{\frac{delta}{2}}}} & (4)\end{matrix}$

If the DC current is less than the calculated value in equation (4),then the Corrective_(dutycyle) is the following calculation:Corrective_(dutycyle)=0  (5)therefore no correction is applied to the duty cycle, at step 410.

If the DC current is greater than the calculated value in equation (4),then the determined corrective duty cycle is calculated in the followingequation:

${Corrective}_{dutycycle} = {\frac{{DC}_{deadtime}}{I_{delta}} \times {{sgn}\left( I_{DC} \right)} \times \left( {I_{ripple} - I_{\frac{delta}{2}} - {I_{DC}}} \right)}$wherein the corrective duty cycle is adjusted and applied to the boostconverter to reduce and/or remove voltage spikes at the boost converteroutput at step 412.

FIG. 6 depicts an exemplary graph of a corrective duty cycle for a boostconverter according to one or more embodiments of the presentapplication. The graph depicts one or more transition regions for theduty cycle current in the boost converter in which the x-axis is theduty cycle average current and the y-axis is the corrective duty cyclefunction.

The positive deadtime as corrective duty cycle 501 represents thecorrective duty cycle value added on top of the desired duty cycle in atransitional region for the boost converter to take into account thedeadtime effect as shown by equation (3) above. In relation to thecorrective duty cycle value, the actual duty cycle for the boostconverter increases as the current through the inductor becomespositive. Therefore the actual duty cycle of the boost converterincreases when the inductor current is positive.

The slew corrective duty cycle 502 and 506 represent the corrective dutycycle when the current value is less than

${I_{ripple} + I_{\frac{delta}{2}}},$and greater than

$I_{ripple} - {I_{\frac{delta}{2}}.}$After determining if the current is positive or negative based on theone or more equations described above, the system may then determinecorrective duty cycle ramp to smooth out the duty cycle in atransitional region. The corrective duty cycle ramp may prevent suddenchanges in the duty cycle based on the corrective value calculated. Theramp allows for a smooth transition.

The corrective duty cycle is zero 504, as shown in equation (5), whenthe DC current is less than the calculated value in equation (4).

The negative deadtime as corrective duty cycle 508 is represented on thegraph that depicts a negative corrective duty cycle added as shown byequation (3). The duty cycle command increases when the current throughthe inductor is negative.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

What is claimed is:
 1. A method comprising: in response to a magnitudeof input current for a boost converter being greater than a sum of aripple current magnitude through an inductor of the boost converter anda predetermined value, correcting by a controller a duty cycle commandfor the boost converter based on a boost converter dead-time and adirection of the input current to drive an output voltage of the boostconverter to a commanded value.
 2. The method of claim 1 wherein theduty cycle command defines transition regions centered at the ripplecurrent magnitude.
 3. The method of claim 1 wherein the duty cyclecommand is corrected such that an actual duty cycle for the boostconverter increases as the current through the inductor becomespositive.
 4. The method of claim 1 wherein the duty cycle command iscorrected such that an actual duty cycle for the boost converterdecreases as the current through the inductor becomes negative.